Digesting lignocellulose with a rosin soap



Patented Jan. 16, 1951 DIGESTING LIGNOCELLULOSE WITH A ROSIN SOAI GrantS. Willey, Chicago, Ill., assignor to United States Gypsum Company,Chicago, 111., a corporation of Illinois No Drawing.

6 Claims.

This invention relates to an improved lignocellulose material and to aprocess forits manufacture. More particularly this invention involves a.method of treating ligno-cellulosic fibrous material which results in aproduct of improved properties when used for the production ofsheet-like, as well as other shaped materials, by the use of heat andpressure.

It has been found that an improved molded product can be formed by thesimultaneous pressing and heating of a sheet of ligno-cellulosicmaterial, if the fibers so treated have been previously cooked in waterunder pressure. If the proper cooking procedure is followed, thestrength and water resistance are greatly improved. While this method oftreatment produces a substance, when formed by heat and pressure into asheet, having properties which are an improvement over that formed fromligno-cellulosic material not so treated yet it has been found that thesheets so formed are brittle and that the yield is considerably reduced.

It has been found that the yield and brittleness can be improved if thecooking of the lignocellulose material is not carried to the point thatsubstantially all of the hemicellulose is removed. This point appears tobe when the yield on a bone dry basis is 70% or over. However, when thissemi-cook is made, preferable to giving a bone dry yield between 80 to90% the resistance to water penetration is considerably less than for amore complete cook such as will be shown by the lower yield. This can beovercome by adding a high percentage of a water proofing material in amanner which will be subsequently set forth.

The usual method of improving the water resistance of fibers is by theaddition of rosin size or similar water proofing material to the pulpeither in the beater or in the stuff chest followed by the addition ofan acid generating material such as alum to effect the precipitation ofthe rosin soap upon the fibers. This method of water proofing ispractical only to a limited extent in the production of hardboard. Itcan not be used to add the quantities needed to give the waterproofnessneeded for many purposes. By practicing this invention it is possible toattain a marked improvement in the water resistance as well as othercharacteristics of a heat and pressure consolidated product formed fromcooked wood such as hardboard by a simplified and economical procedure.

Hardboard is a sheetlike commercial product 5 abietic acid or rosin.Rosin size is preferred Application February 14, 1944, Serial No.522,395

obtained by compressing fibers into a hard dense sheet by the use ofheat-with pressure, preferably to a density of'between 40 to lbs. percu. ft. Its strength and water resistance resembles wood but it is muchmore uniform in properties than wood. Since the manufacture of hardboardis one of the outstanding purposes for which this invention can be used,it will be used in the forthcoming examples of means by which thisinvention may be carried out. Such use is only exemplary as othermaterial which are not sheetlike in form can be made following thispatent.

It is the purpose of this invention to disclose a heat and pressureconsolidated product, especially hardboard, which has propertiessuperior to those produced in the past, such, for example, as improvedpressing characteristics, minimized efllorescenses, less tendency todisintegrate with age, much less brittleness and a relatively highstrength and resistance to water absorption. While an improved productis formed by this invention, it is also an object of this invention toshow means by which such a product can be obtained by a. more economicaland simplified method.

In the cooking of ligno-cellulosic material such as wood, particularlythose known as hard wood, with water, there are formed acids which arediscarded and generally are not used for any commercial purpose. It, isone of the objects of this invention to utilize these acids in thewaterproofing of the fibers by the precipitation of the waterproofingmaterial from solution so that it becomes an integral part of the fiberssimultaneously as the fibers are being cooked under pressure. It hasbeen found that when the Waterproofing material is added to thedigester, such as with the water to be used for cooking, the acidsformed during the decomposition of the woods causes it to precipitatewhence, it becomes associated with the fibers.

For the purpose of illustration and to describe a preferred embodimentof this invention, a waterproofing material is selected as an examplewhich is commonly used in the art, and known as rosin size orsubstantially sodium abietate. However, it is not the intention to limitthe scope of this invention thereby as other waterproofing materialswhich are precipitable by acids can be utilized. Examples of suchmaterials are the sodium, potassium or ammonium soap of the saturated orunsaturated fatty acids as well as because of its lower cost,effectiveness and its adaptability to the process.

In carrying out this invention it is preferred to use the cookingprocedure disclosed in a copending patent application, Serial Number461,388, now abandoned, the subject of a separate invention and filedjointly with another inventor.

The wood to be utilized for the purpose of this invention can be eitherhard or soft wood. or a mixture of the two. The woodsuch for example ascottonwood or willoWis first debarked by any suitable means, or the barkcan be left on if desired, and then comminuted such as into chips aboutthe size used in the manufacture of chemically cooked wood pulp. Anexcellent size of chip for this purpose is one having dimensions ofapproximately one inch by two inch by one-quarter inch. These chips arecharged into a suitable digester capable of withstanding the intendedpressure. A completely enclosed vessel of the well known spherical typeis excellent for this purpose. After the wood chips have been chargedinto the vessel or digester a suilicient amount of water is added tobring the ratio of wood chips to water about equal to two parts of waterto one of dry wood. The desired quantity of rosin size can then beadded. Five per cent on the basis of the bone dry wood will give goodresults though in many cases only one per cent is sufficient. The rosinsize can be any commercial grade as commonly used in the trade: it maybe found desirable, in order to facilitate complete intermixing of therosin with the digesting liquor, to first add the rosin size to waterbefore adding to the digester. The digester is then heated externally orby the addition of steam or both.

If desired a very high percentage of rosin size can be added to obtainfurther improvement in properties. This is entirely possible by thismethod; amounts as high as 12% or more can be added. If pulp is used,instead of chips, the ratio of water used should be increased such as to5 parts of water and 1 part of bone dry pulp.

It may be found expedient from the commercial standpoint to heat rapidlyto the desired temperature and pressure and then hold at this point forthe required time. A slower method of heating is preferred, if possible,as it allows a greater penetration of the rosin size into the fibrousmaterial before it is precipitated by acids generated by cooking. Afterthe desired temperature has been reached for carrying on the cooking,the time required to complete the treatment is a function of the size ofthe chips as well as that of the pressure used.

When the cooking is carried out under steam pressure it is preferred touse temperatures rather than pressu'e, to control the heating operationsas the presence of air or other gases, within the digester, may soinfluence the pressure that the temperature obtained is not thatcorresponding to saturated steam at the pres-- sure indicated. Becauseof this, it is always desirable to release the digester before it hasfinally reached its temperature to remove the air or gases. The usualtime to release the digester is at a temperature slightly over 212 F.

It has also been discovered that, besides entrapped air, there-is also adecomposition of part of the wood into gases under certain conditionsHOWEVBI', whenever the heating has proceeded to the point where anappreciable quantity of gases are generated, it has proceeded too far togive the most optimum all around results. Hence, it is desirable not tocarry on the digesting operation any further than is necessary; and theformation of a generous quantity of gas is a sure sign that theoperations have been carried too far and should be stopped immediately.One of the purposes of cooking the wood is to decompose the pentosans,or the non-lignin and the non-cellulosic elements, contained in thewood. The lignin and cellulose portion of the wood are its most,valuable constituents and to destroy them would be defeating one of theobjects of this invention.

A range of temperatures from 335 to 385 F. and time from one half to oneand one-half hours have been found very satisfactory for chips of thesize used in the paper industry, such as about one by two by one-quarterinches. Slight adjustments in the time and temperature conditions canreadily be made in order to give the best pulp from the kind and size ofnatural lignocellulose material and digester used. For the size of chipsreferred to above and for willow, a cook of 45 min. at 340 F. issatisfactory. The higher the temperature used, the lower the timerequired for cooking, but in general it has been found that betterresults are obtained at the lower temperature.

When the chips are properly cooked they retain their shape and upon mildrefining produce a pulp which is fibrous in nature rather than mushy. Inother words, a relatively free pulp can be produced which is strong andeasy to felt. It will be found that the chips cooked with rosin size asdescribed above will be more fibrous and stronger than when not socooked and still the yield is higher.

The wood should, therefore, only be cooked sufficiently to generateenough acid to precipitate the rosin size and to destroy a portion ofthe hcmi-cellulose or non-lignin or cellulose material present in thewood. A "raw cook" is preferred. A measure of the proper cook can :bestbe made by the yield of wood obtained after the cooking operation. Ifthe yield is between and based upon bone dry weights of the pulp alone,the most desirable results have been obtained. A yield as low as 70% isundesirable. It is one of the purposes of this invention to only cooksufficiently to obtain the desirable properties of a water cooked pulpwith the minimum of the disadvantages. It has been found thatsubstantially all of the desirable properties can be obtained by a rawcook that is one giving a yield of from substantially 80 to 90% basedupon the bone dry pulp. The strength and water resistance areappreciably improved, while the yield is good and there is littletrouble with brittleness. However, for many purposes it will be foundthat the water absorption of the finished product will be too high, andto lower this the addition of some sort of sizing material is necessary.As mentioned above, the usual method of improving the water resistance,such as by the addition of rosin size to the beater, has manydisadvantages when applied to hardboard manufacture.

Some of these disadvantages are: Only a small quantity can be addedbecause of difliculty in forming due to gumming up of the felts andforming equipment and to blisters and sticking during pressing when alarge quantity of size is used. Also, there is a marked tendency forboard formed from sheets sized in this manner to produce anefilorescence due to discoloring soluble 5. salts appearing upon thesurface of the sheet. By following this invention and adding thematerial to improve the water resistance to the cooker before or duringthe operation, a marked The pulp is then diluted with water to aconsistency of from one-half to one per cent of dry fiber, preferablywith the pH still maintained at 4.8. This pulp is formed into a coherentsheet improvement in water resistance is'noticeable upon some type ofboard forming machine such alon with increased strength. A the ygs is asa rotary cylinder or a Fourdrinier. The thickr. and Since very littlesodium sal are ness of the sheet is usually from one-half to presentafter washing very little efllorescence will n a one-half h dependingupon the be noticed. In additiomthe fibers will be tougher finalthickness of the consolidated board to be and hence inamore d sirablstat tofcrm amat made. However, it is within the scope of this p p oryfor p ss g. s e 0! the invention to form a thin mat, and to use severalsenses of this invention is to form it tough, stron layers, along witha, suitable adhesive, to make il ldg ll hog h ki ce 201 ga fi g a singlesheetlike product. The extraneous moision y s y 000 us a na ura 8 11 05ture is removed from the-sheet by first passing n i s y g h z i t g 15through suitable press rolls and then into a dryer 0 a Web r 62 en ma Ierew in which the remaining moisture is removed by Wa'ter repellentmaterial is Precipitated. by the the use of heat. The dried sheet or matis then' d fo during E- u transferred to a suitable press with platensby After the cooking period'has elapsed the b0 which the mat isconsolidated with pressures i333; i ti to gg vzi' i; grc i i i t s r fiiigu i i about to abolt 2500 P n per square nc l, epend rig upon hedensitydesired, and a 18 acidic and is dark in color. It is desirable t;a temperature range of from to about remov? the cook liquor z t Thepressing time at a lower range of temperathe chlps Several times w th waa a ture may be from ten to twelve minutes while of ime may e only a fewseconds. The olowing cause stlckmg m the press and the g a conditionshave been found satisfactory in makgzgig ffigi gg on the Surface of t emus 8 ing strong sheetlike material known as hardboard from a dried matprepared as described above: g p g g gi gg ggg fi temperature 450 F.,pressure 800 lbs. per square pu p 33.8" i th mtar dis The inch, time 2minutes. Under these conditions a 225 2 2 a gloreeeasfly g gg the boardhaving excellent dry and wet strength is natural bond between the fibershave been produced p prepared as descnbed e loosened. The fibersthemselves have not been This hardboard W111 be found be Superior toappreciably changed, but will be found to be one prepared from fibersmade in the usual mam highly water resistant, part of which is due tothe waterproofing action attained by the above i is alsohwlthm the scopeof Invention to described procedura ho press t e wet mat, using a wirescreen with The pulp can be'washed and deckered if def gn k g i z i g ggi g i i (115' sired, after first removingoversized chips and 40 g g h 0a dirt by screening, or the pulp can be run directly t M of ma ena n E gower to the stuff chest. Water is added to bring the empera a Pressuremay 8 use m an consistence of the pulp to between 3 to 4 increase intime is necessary because of the cent. Other materials can be added atthis time amount of molswre "3 be removed; Obviously to the pulp ifdesired such as drying 011s dyes other methods of forming the fiber intoa sheet, fillers m as well as other methods of pressing or consoli- Itwill be found that none of the above procesdating t fi s o a dSubstance, y be sing of the fibers will remove the rosin size which usedand still be within the scope of this inappears to be firmly adhered tothe fibers in some vention. unexplainable manner after precipitation.For The hardboard after pressing is cooled and igg gg g fg gggfggfigg1ifi3g stored under conditions permitting it to normalizeaccording to the moisture content of the air. t l' l fil i e gli fli pii xfr fai ly zg -ig If desired, it may be trimmed and sized before it isdesirable to add an acidic material such as g rg It Is ready Sale and8111p" sulphuric acid, alum or ferric sulphate to the e I stuff chest tobring the pH to It will also be The following table clearly illustratesthe imfound that owing to the absence of a substantial proved Opertlesattamed by coPkmg hardwood quantity of alkaline salts, a much lessquantity p p w t a w fing ma rial such as rosin of acid will be needed.size:

Vftater absorp- 1011 0! can s g? v e; the; ists" 55 with? Water cu. ft.soaking 24 lbs./sq. in.

hrs. F.

1 Noneused N15 dacd 70.4 48.7 7,620 5% during cooking--- sime nl- 71.212.8 7,850 Noneused 5 71.3 20.7 7,435 5% during cooking 5 71. 2 9. 4 8,078 None usedl2% 4.8...... 68.2 as 6,890

added to the beater. 12% during cooking... 4.5 68.9 9.1 7, 710

The above were all prepared under similar conditions and are accuratecomparative results. Considerable trouble was encountered with blistersand sticking with No. and it was only with great difliculty that asuitable hardboard was obtained for testing purposes.

As shown above, the addition of the rosin size to the digester duringthe cooking of the pulp improves the water absorption. In addition tothese, other advantages of great importance to the quality-of theresultant product formed are obtained, one particularly being theformation of a tough non-brittle hardboard.

An outstanding advantage of this method of treating fibers used inmanufacturing products formed by consolidating with heat, and pressureis that no additional alum or acidic material is required to precipitatethe Water proofing material upon the fibers. The waterproofing materialhas already been precipitated upon the fibers in the digester by theacids formed during cooking. However, as pointed out previously, it ismore advantageous from the water resistance standpoint to reacidify thepulp after washing and before the formation of the mat. However, if anacid is not used, the white water will not be acidic, a very desirableadvantage from the operating standpoint. Also, the product formed byconsolidating with heat and pressure is not substantially acid, so thatits deterioration with age should be less. It is well known that fibroussheets which are highly acidic deteriorate more rapidly with age thanthose which are substantially neutral. While the water resistance of anon-acid sheet will be considerably higher than wood not cooked with thewaterproofing material, it still will not be as good as if it had beenacidified, though in some cases the improvements in other properties mayoutbalance the lower water resistance.

Another outstanding advantage obtained by following the principles setforth in this invention is the elimination, or at least a verysubstantial reduction, of efllorescence upon the surface of thehardooard. Efilorescence is the migration of soluble salts to thesurface of the fibrous sheets in such concentration that theirappearance can be readily detected upon the surface. The whitediscoloration presents an unattractive appearance, and it is alwaysdesirable to prevent its formation, if possible. Certain atmosphericconditions, particularly those in hot humid climates, brin out thissituation more markedly. Since under this invention the sizing takesplace in the digester, most of the soluble alkali salts such as sodiumsulfate which were formed during the sizing operation are removed bywashing, hence there is very little of this material remaining tocontribute to efllorescence. This is true even when the pulp is madeacidic after washing out the digester liquor, for the acid can be suchas not to contribute to the formation of soluble salts, such for exampleas the use of alum, ferric sulphate or sulphuric acid.

One outstanding property of hardboard made from ligno-cellulosic fibrousmaterial, such as wood, cooked in accordance with the principles :rtforth in this example is its excellent bending and shaping properties.Bends can be made substantially free from cracks under conditions whichwould cause cracking as well as other difficulties in the bending ofhardboard prepared in a manner not in accordance with this invention.

Besides the advantages of improvement in the properties of the hardboardand other products.

produced following this invention, over those of the prior art, thereare also marked process improvements some of which are enumerated below.For example, the addition of the waterproofing material to thecookergreatly facilitates the control and introduction of the materialinto the pulp, as the amount. of size can be added more easily and canbe accurately controlled. It is much more expedient to add thewaterproofing material to a digester than it is to add it continuouslyto pulp as is now the practice.

A more important advantage is that by treating cooked fiber as disclosedin this invention, it is possible to use-a much greater quantity ofrosin size than if it was added after cooking, without danger ofsticking or blistering during the pressing of the sheets. Also, a highpercentage of such material added to .the pulp after cooking anddisintegrating results in a serious problem in the formation of the wetmat. Such difficulties as excessive foaming, gumming up of the felts andforming cylinders are encountered. Sheets containing as much as 12%rosin size have been formed, dried and pressed without difficulty byadding the size to the digester. With 12% of rosin size added afterWashing the felts andcylinders would become gummy and sticky, the sheetswould be slow in forming and practically every sheet pressed would haveblisters and stick in the press.

Other advantages not mentioned will readily occur to those skilled inthe art of which this invention is a part. Likewise, numerousmodifications and alterations can be made in this invention withoutdeparting from its essence. Various changes can also be made in thematerials used, such as the use of soft woods instead of hard-"' woods.It is also possible to apply this invention to the preparation of pulpfrom straw, bagasse, and other fibrous materials containingligno-cellulose.

It is not clear exactly what takes place when ligno-cellulosic materialsare cooked with a waterproofing material such as rosin size. One theoryis that there is a combination of the free acid with theligno-cellulosic material in some manner, which enables it to stayadhered to the fibers in a way which will permit processing without thedisadvantage usually experienced when the addition is made to the pulpafter its preparation. A resinous product appears to be present as theproperties of the fibrous material when subjected to heat and pressureappear to be-altered in a manner to indicate the presence of such amaterial, The precipitated material is very diflicult to separate fromor identify with the fibers when cooked therewith, though tests haveestablished its presence. While it is difficult to identify thewaterproofing material, it can not be accounted for in any other mannerthan being in some way associated with the fibers and is not lost in thedigester liquors.

By rosin it is meant any of the materials commonly classified as rosinor related to resin, such for example as hydrogenated rosin,disproportionated rosin, polymerized rosin, heat treated rosin, rosinoil, rosin acids or any of the color grades of rosin as known in theart, or a mixture of these materials with other materials such as thefatty acids. 'Also, it is not the intention to limit this invention to arosin type of material for obviously the principles of this inventioncan. be advantageously applied to other types of waterproofing materialswhich can be applied in liquid form by saponirying or other means whichwill give a precipitation with the acids formed during cooking, such forexample as the soluble soaps of saturated or unsaturated fattyacids,'drying oils, etc. Throughout this application the term s1ze"is tobe construed to mean any waterproofing material in saponified .formwhich will be precipitated by an acid. In such cases it may be foundmore advantageous to apply the materials in emulsion form such asmentioned previously. It is not necessary that all of the availablematerial be neutralized; only enough to enable introduction to thedigester. It is within the scope of this invention to add the saponifiedor acid precipitable material to the digester at any time during thecooking operation, which will give. the best results. The material canbe added near the end of the cook if desired. It is also within thepurpose of this invention to control the rate or time of precipitationby adding acid or alkaline material to the digcster. If an alkalinematerial such for example as 1% of NaOH is added to the digester alongwith acid precipitated material, the acids formed during the cooking ofthe wood are partially neutralized and the precipitation is retardedthus permitting a greater. penetration into the wood.

By way of summary this invention covers the preparation of an improvedstronger and more fibrous pulp material suitable for the preparation ofarticles molded under heat and pressure par- 1 material removedtherefrom and substantially free from efllorescent salts, consisting ofdigesting at a temperature of 335 F. to 385 F. for V2 to 1 /2 hours, acomminuted natural ligno-celluticularly from fibrous mats, such ashardboard,

by cooking ligno-cellulosic material with water along with awaterproofing material such as rosin in saponified or emulsified form inwhich the generation of an acid during cooking will cause aprecipitation upon and into the fibers along with a possible reactiontherewith, the exact nature of which is not clear. The product thusobtained has superior properties such as higher strength and waterresistance, improved bending and shaping characteristics substantiallyno efliorescence along with certain operating advantages, such aspermitting a higher percentage of treating material to be used withoutdanger of sticking or blisters forming during pressing and enabling amat containing a high percentage of sticky sizing material to be readilyformed without any appreciable slowing up of formation because offoaming or gumming up of the felts or to a decrease in freeness. Thispulp has the further advantage that if a pH of around 5 is desired itcan be attained with a much lesser amount of acidic material and withvery little danger of forming soluble sodium salts. Because of thegreatly improved water resistance obtained in hardboard formed from pulptreated in accordance with this invention, the cook ng need not becarried as far, thus increasing the yield and improving the toughnessand strength of the fibers over the full and complete cook. Co kingoperation which will give a yield of 80-90% is .sufiicient andpreferred.

Having disclosed a practical embodiment of this invention and specificexamples, theories and uses which are given to insure a clearunderstanding of the essence of this invention, it is not the intentionto be limited thereby for obviously many variations may be made by thosesk lled in the art and still be within the scope of this invention whichis only limited in extent by the forthcoming claims.

It is claimed:

1. The method of producing a sized heat and pressure consolidatedligno-cellulosic product having a substantial quantity of water s 1losic material with about one to five parts by weight of watercontaining as the essential component .01 to .12 parts by weight, basedupon the bone-dry ligno-celiulosic fiber, of an aqueous dispersedpyroligneous acid precipitable soap selected from the group consistingrespectively of ammonium, sodium and potassium soaps of rosin acid untilan acid pH is attained and until at least a portion of thehemi-cellulosic material has been removed from said naturalligno-cellulosic material and washing said cooked comminutedligno-cellulosic material substantially free from cooking liquor,further disintegrating said fibers into a pulp, forming said pulp into ashape substantially similar to said desired product and consolidatingsaid shape under heat and pressure into said product.

2. The process claimed in claim 1 in which said soap of a rosin acid isrosin size.

3. The method of forming an improved sized hardboard of high strengthand water resistance and substantially free from efllorescenceconsisting of cooking with about one to five parts by weight of water ata temperature of 335 to 385 F. at /2 to 1%.; hours, a comminuted naturallignocellulosic material, said water containing as the essentialcomponent .01 to .12 parts by weight, a l parts based upon the bone-dryligno-cellulosic fiber, of an aqueous suspension of an acid precipitablewaterproofing material selected from the group consisting respectivelyof the alkali metal and ammonium soaps of rosin acid, for a sufficientlength of time to obtain a bone-dry yield of from to and to precipitatesaid waterproofing material by autogenously generated pyroiigneousacids, removing the liquor from said cooked ligno-celulosic material,further disintegrating said cooked ligno-cellulosic material intopulp-like fibers, washing said fibers to remove substantially all thewater soluble materials, forming said fibers into a sheet, drying saidsheet and consolidating said sheet under heat and pressure.

4. The method of forming an improved hardboard of high strength andwater resistance and improved bending and non-brittleness propertiesconsisting of digesting at a temperature of 335 F. to 385 F. for to 1 /2hours disintegrated natural ligno-cellulosic material in an aqueoussuspension of about one to five parts water containing as the essentialcomponent between .01 to .12 parts by weight, all parts based on bonedryligno-ce'lulosic material, of a waterproofing sizing material selectedfrom the groupv consisting respectively of the alkali metal and ammoniumsoaps of a rosin to obtain a bone-dry yield of from 80% to 90% and toautogenously generate pyroligneous acids to precipitate said sizingmateria, removing a substantial portion of the spent cooking liquors,further disintegrating said cooked ligno-cellulosic material into afiber, forming said fiber from an aqueous suspension into a wet la andsimultaneously heating and pressing said lap with a foraminous surfaceon at least one face, whereby the water contained therein escapes duringsaid pressing operation, until said wet lap has dried.

5. The process claimed in claim 4 in which said waterproofing sizingmaterial is rosin size.

6. The process of producing a hardboard type 5 P oduct having a densityof substantially between 11 40 and 80 lbs. per cubic foot consisting ofcooking a comminuted natural wood-like ligno-cellulosic material withbetween about one to five parts by weight of water containing as theessential component dispersed therein from substantially about .01 tosubstantially about .12 parts by weight of said natural wood-likeligno-cellulosic material, based on bone-dry conditions, of a sizingmaterial selected from the group consisting respectively of the alkalimetal and ammonium soaps of a rosin to give a yield substantiallycorresponding to that obtained when said comminuted natural wood-likeligno-cellulosic material is cooked for substantially 45 minutes at 345F. under substantially saturated steam conditions, washing the liquorsfrom said sized, cooked, comminuted natural wood-like ligno-cellulosicmaterial, refining said cooked material to a fibrous form, washing saidfibers with water to remove readily soluble substances, diluting saidwashrsl refined fibers with water, adjusting the pH of said washed pulpto an acid pH, forming said diluted pulp into a shape similar to theshape of said finished hardboard, drying said shape to substantially abone-dry condition and then consolidating at a temperature substantiallybetween 350 and 560 F. and at a pressure of substantially between 500and 2500 pounds per square inch, and from substantially twenty minutesto ten seconds, the shorter time used with the higher temperature, toform said hardboard product.

GRANT S. WILLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,633,738 Fish June 28, 19271,682,834 Dedricl: Sept. 4, 1928 1,786,462 Stryker Dec. 30, 19301,873,056 Smith Aug. 23, 1932 1,945,862 MacIntyre Feb. 6, 1934 2,047,170Asplund July 14, 1936 2,056,810 Smyser -Oct. 6, 1936 5 2,247,204Schorger June 24, 1941 2,247,206 Schorger June 24, 1941 2,292,389 MeilerAug. 11, 1942 2,292,390 Meiler Aug. 11, 1942 2,317,394 Mason Apr. 27,1943 2,375,414 Heritage May 8, 1945 2,402,160 Heritage June 18, 1946FOREIGN PATENTS Number Country Date 82,438 Austria Jan. 25, 1921 649,669France May 26, 1914 35,854 Germany June 10, 1886 314,146 Germany Aug.30, 1919

1. THE METHOD OF PRODUCING A SIZED HEAT AND PRESSURE CONSOLIDATEDLIGNO-CELLULOSIC PRODUCT HAVING A SUBSTANTIAL QUANTITY OF WATER SOLUBLEMATERIAL REMOVED THEREFROM AND SUBSTANTIALLY FREE FROM EFFFORESCENTSALTS, CONSISTING OF DIGESTING AT A TEMPERATURE OF 335* F. TO 385* F.FOR 1/2 TO 11/2 HOURS, A COMMINUTED NATURAL LIGNO-CELLULOSIC MATERIALWITH ABOUT ONE TO FIVE PARTS BY WEIGHT OF WATER CONTAINING AS THEESSENTIAL COMPONENT .01 TO .12 PARTS BY WEIGHT, BASED UPON THE BONE-DRYLIGNO-CELLULOSIC FIBER, OF AN AQUEOUS DISPERSED PYROLIGNEOUS ACIDPRECIPITABLE SOAP SELECTED FROM THE GROUP CONSISTING RESPECTIVELY OFAMMONIUM, SODIUM AND POTASSIUM SOAPS OF ROSIN ACID UNTIL AN ACID PH ISATTAINED AND UNTIL AT LEAST A PORTION OF THE HEMI-CELLULOSIC MATERIALHAS BEEN REMOVED FROM SAID NATURAL LIGNO-CELLULOSIC MATERIAL AND WASHINGSAID COOKED COMMINUTED LIGNO-CELLULOSIC MATERIAL SUBSTANTIALLY FREE FROMCOOKING LIQUOR, FURTHER DISINTEGRATING SAID FIBERS INTO A PULP, FORMINGSAID PULP INTO A SHAPE SUBSTANTIALLY SIMILAR TO SAID DESIRED PRODUCT ANDCONSOLIDATING SAID SHAPE UNDER HEAT AND PRESSURE INTO SAID PRODUCT.